The use of intercept messages to explain why a call cannot be completed is known in telephony. Such intercept messages are typically initiated whenever an outgoing call cannot be completed for various reasons, such as the called number being out of service, changed, or not being a working number. The person who made the call receives a recorded audio message advising that the call was not completed as dialed.
Intercept messages according to the known prior art are typically delivered at the switching office where the need for intercept has been detected, usually the central office where the dialed number would have been connected as a subscriber. The appropriate intercept message is returned along a trunk circuit to the originating office, so that the calling party can receive the message.
Despite the widespread acceptance of electronic switching systems (ESS) for central offices, there are still a number of central offices employing electromechanical switching equipment such as step by step or crossbar type switches. These types of central offices are often associated with smaller, non-Bell System local operating companies, as well as Bell operating companies. Traditionally, electromechanical (EM) central offices have relied upon use of operator intervention to tell a calling party that the called number has been changed to a new number. This is called ONI, for operator number identification. Alternatively, some EM offices use a fixed message intercept machine, wherein all intercepted calls receive the same predetermined generic announcement that a number has been changed, without providing the calling party with the new number. In the case of the fixed message intercept machine, the calling party must call directory assistance to obtain the new number.
There are commercially available changed-number intercept systems, also known as "automatic intercept systems" (AIS) for modern digital electronic switching system (ESS) central offices, such as the type IIS intercept system manufactured by The Audichron Company, Atlanta, GA, assignee of the present invention. Modern AIS are responsive to a multifrequency (MF) digit stream containing the digits of the called telephone number, and provide an intercept message appropriate for that number, e.g., that it is out of service, or has been changed to a new number (which is then provided in audio form to the calling party). A particular difficulty in providing changed number intercept for EM offices is that there is no apparatus for identifying the called telephone number for the AIS. Thus, most EM central offices cannot provide automatic number identification (ANI) for intercepted calls, and must still rely on operator intervention for ONI.
As telephone companies having EM central offices grow, they are upgrading their systems to ESS type central office equipment. However, this type of equipment is expensive. Moreover, a network having some ESS switching equipment and some EM switching equipment in satellite central offices sometimes is incompatible. Often, the ESS will have ANI intercept equipment such as the AIS, which may provide considerable excess intercept handling capability. This intercept capability cannot be fully used until the satellite central offices are upgraded to ESS type equipment. While the ESS equipment is readily able to work with its own AIS, it is less than desirable to provide some customers with ANI but others with ONI. It would be preferable to have a low cost, intermediate method for providing ANI for satellite EM central offices, without requiring that the smaller telephone company upgrade all its central offices to ESS at once. Such is provided in the present invention.